1 /* 2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, you can access it online at 16 * http://www.gnu.org/licenses/gpl-2.0.html. 17 * 18 * Copyright IBM Corporation, 2008 19 * 20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 21 * 22 * For detailed explanation of Read-Copy Update mechanism see - 23 * Documentation/RCU 24 */ 25 #include <linux/completion.h> 26 #include <linux/interrupt.h> 27 #include <linux/notifier.h> 28 #include <linux/rcupdate_wait.h> 29 #include <linux/kernel.h> 30 #include <linux/export.h> 31 #include <linux/mutex.h> 32 #include <linux/sched.h> 33 #include <linux/types.h> 34 #include <linux/init.h> 35 #include <linux/time.h> 36 #include <linux/cpu.h> 37 #include <linux/prefetch.h> 38 #include <linux/trace_events.h> 39 40 #include "rcu.h" 41 42 /* Forward declarations for tiny_plugin.h. */ 43 struct rcu_ctrlblk; 44 static void __call_rcu(struct rcu_head *head, 45 rcu_callback_t func, 46 struct rcu_ctrlblk *rcp); 47 48 #include "tiny_plugin.h" 49 50 void rcu_barrier_bh(void) 51 { 52 wait_rcu_gp(call_rcu_bh); 53 } 54 EXPORT_SYMBOL(rcu_barrier_bh); 55 56 void rcu_barrier_sched(void) 57 { 58 wait_rcu_gp(call_rcu_sched); 59 } 60 EXPORT_SYMBOL(rcu_barrier_sched); 61 62 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) 63 64 /* 65 * Test whether RCU thinks that the current CPU is idle. 66 */ 67 bool notrace __rcu_is_watching(void) 68 { 69 return true; 70 } 71 EXPORT_SYMBOL(__rcu_is_watching); 72 73 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ 74 75 /* 76 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 77 * Also irqs are disabled to avoid confusion due to interrupt handlers 78 * invoking call_rcu(). 79 */ 80 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 81 { 82 RCU_TRACE(reset_cpu_stall_ticks(rcp)); 83 if (rcp->donetail != rcp->curtail) { 84 rcp->donetail = rcp->curtail; 85 return 1; 86 } 87 88 return 0; 89 } 90 91 /* 92 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 93 * are at it, given that any rcu quiescent state is also an rcu_bh 94 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 95 */ 96 void rcu_sched_qs(void) 97 { 98 unsigned long flags; 99 100 local_irq_save(flags); 101 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 102 rcu_qsctr_help(&rcu_bh_ctrlblk)) 103 raise_softirq(RCU_SOFTIRQ); 104 local_irq_restore(flags); 105 } 106 107 /* 108 * Record an rcu_bh quiescent state. 109 */ 110 void rcu_bh_qs(void) 111 { 112 unsigned long flags; 113 114 local_irq_save(flags); 115 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 116 raise_softirq(RCU_SOFTIRQ); 117 local_irq_restore(flags); 118 } 119 120 /* 121 * Check to see if the scheduling-clock interrupt came from an extended 122 * quiescent state, and, if so, tell RCU about it. This function must 123 * be called from hardirq context. It is normally called from the 124 * scheduling-clock interrupt. 125 */ 126 void rcu_check_callbacks(int user) 127 { 128 RCU_TRACE(check_cpu_stalls()); 129 if (user) 130 rcu_sched_qs(); 131 else if (!in_softirq()) 132 rcu_bh_qs(); 133 if (user) 134 rcu_note_voluntary_context_switch(current); 135 } 136 137 /* 138 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 139 * whose grace period has elapsed. 140 */ 141 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 142 { 143 const char *rn = NULL; 144 struct rcu_head *next, *list; 145 unsigned long flags; 146 RCU_TRACE(int cb_count = 0); 147 148 /* Move the ready-to-invoke callbacks to a local list. */ 149 local_irq_save(flags); 150 if (rcp->donetail == &rcp->rcucblist) { 151 /* No callbacks ready, so just leave. */ 152 local_irq_restore(flags); 153 return; 154 } 155 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 156 list = rcp->rcucblist; 157 rcp->rcucblist = *rcp->donetail; 158 *rcp->donetail = NULL; 159 if (rcp->curtail == rcp->donetail) 160 rcp->curtail = &rcp->rcucblist; 161 rcp->donetail = &rcp->rcucblist; 162 local_irq_restore(flags); 163 164 /* Invoke the callbacks on the local list. */ 165 RCU_TRACE(rn = rcp->name); 166 while (list) { 167 next = list->next; 168 prefetch(next); 169 debug_rcu_head_unqueue(list); 170 local_bh_disable(); 171 __rcu_reclaim(rn, list); 172 local_bh_enable(); 173 list = next; 174 RCU_TRACE(cb_count++); 175 } 176 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 177 RCU_TRACE(trace_rcu_batch_end(rcp->name, 178 cb_count, 0, need_resched(), 179 is_idle_task(current), 180 false)); 181 } 182 183 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) 184 { 185 __rcu_process_callbacks(&rcu_sched_ctrlblk); 186 __rcu_process_callbacks(&rcu_bh_ctrlblk); 187 } 188 189 /* 190 * Wait for a grace period to elapse. But it is illegal to invoke 191 * synchronize_sched() from within an RCU read-side critical section. 192 * Therefore, any legal call to synchronize_sched() is a quiescent 193 * state, and so on a UP system, synchronize_sched() need do nothing. 194 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 195 * benefits of doing might_sleep() to reduce latency.) 196 * 197 * Cool, huh? (Due to Josh Triplett.) 198 */ 199 void synchronize_sched(void) 200 { 201 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 202 lock_is_held(&rcu_lock_map) || 203 lock_is_held(&rcu_sched_lock_map), 204 "Illegal synchronize_sched() in RCU read-side critical section"); 205 } 206 EXPORT_SYMBOL_GPL(synchronize_sched); 207 208 /* 209 * Helper function for call_rcu() and call_rcu_bh(). 210 */ 211 static void __call_rcu(struct rcu_head *head, 212 rcu_callback_t func, 213 struct rcu_ctrlblk *rcp) 214 { 215 unsigned long flags; 216 217 debug_rcu_head_queue(head); 218 head->func = func; 219 head->next = NULL; 220 221 local_irq_save(flags); 222 *rcp->curtail = head; 223 rcp->curtail = &head->next; 224 RCU_TRACE(rcp->qlen++); 225 local_irq_restore(flags); 226 227 if (unlikely(is_idle_task(current))) { 228 /* force scheduling for rcu_sched_qs() */ 229 resched_cpu(0); 230 } 231 } 232 233 /* 234 * Post an RCU callback to be invoked after the end of an RCU-sched grace 235 * period. But since we have but one CPU, that would be after any 236 * quiescent state. 237 */ 238 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) 239 { 240 __call_rcu(head, func, &rcu_sched_ctrlblk); 241 } 242 EXPORT_SYMBOL_GPL(call_rcu_sched); 243 244 /* 245 * Post an RCU bottom-half callback to be invoked after any subsequent 246 * quiescent state. 247 */ 248 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) 249 { 250 __call_rcu(head, func, &rcu_bh_ctrlblk); 251 } 252 EXPORT_SYMBOL_GPL(call_rcu_bh); 253 254 void __init rcu_init(void) 255 { 256 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 257 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); 258 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); 259 260 rcu_early_boot_tests(); 261 } 262